The author of the letter, mailed from Saxon in the canton of Valais, blames Weber for “taking my job” and destroying his retirement plan, the ATS news agency reported.

Weber, a resident of Montreux in the canton of Vaud, received the letter last week more than 17 months after voters in Switzerland backed his initiative to limit the number of holiday homes in Swiss municipalities to 20 percent.

The anonymous writer of the French-language letter tells Weber “your daughter and your lawyer must die” and gives deadlines of 18 and 24 months respectively.

Two cartridges from a hunting rifle were included in the envelope with the hand-written letter, dated August 12th but posted a week later.

The letter is signed by a “citizen in deep shit”.

“This kind of behaviour is intolerable and we can well see an uncontrolled emotion,” Pierre Chiffelle, Weber’s lawyer, told ATS, confirming a report carried by Le Matin newspaper.

“One cannot act like that,” said Chifelle, who said a complaint was filed last Tuesday with the attorney general of the canton of Valais.

Weber's Helvetia Nostra (“Our Switzerland”) group has successfully campaigned for the protection of environmentally significant places in Switzerland such as Engadine Valley in Graubünden and the Lavaux wine region in the canton of Vaud.

The letter is now in the hands of cantonal police, who are investigating the matter.

But Weber said he is prepared to withdraw the criminal complaint if the letter writer aplogizes in person for what he or she has done, ATS reported.